I have a half mesh front.with a 2.4 roof covering a full length averie.I have 4 2.4 compartments with a mesh door at either end off the shed,with a solid door in front of each.Which is left open when it is not raining.I think the damp is mainly caused by the droppings,as I had one compartment empty last winter which stayed dry while there was no birds in it.But I have no vents along the back of the loft.Any suggestions would be appreciated. Thanks for the reply's so far. Gary.